1. Field of the Invention
The invention relates to a molding apparatus for a resin shielding semiconductor device, a lead frame for the device from which surplus resin can be detached without burrs, and a method for removing without burrs surplus resin attached to a semiconductor device formed using the molding apparatus.
2. Description of the Related Art
A conventional process for encapsulating a semiconductor device with a resin material is shown in FIGS. 6A through 6D. Referring to FIG. 6A, a semiconductor chip 100 mounted on a lead frame 102 is set in a molding apparatus 500. The molding apparatus 500 includes an upper platen 201 and a lower platen 211. The upper platen 201 has a cull 202, an upper resin passage 213a and an upper cavity 203, and the lower platen 211 has a transfer pot 212, a lower resin passage 213b, a gate 214 and a lower cavity 215. The lower resin passage 213b has a rearward region 213b′ and forward region 213b″, which is thinner than the rearward region 213b′. The lead frame 102 is placed between the lower platen 211 and the upper platen 201 as the semiconductor chip is located in the center of the lower cavity 215 and the upper cavity 203. A tablet 301 of the resin material is placed in the transfer pot 212.
Referring to FIG. 6B, the lead frame 102 is placed on the lower cavity wherein one end of the lead frame 102 is sandwiched by the upper and lower cavities 203 and 215, and other end is extended to the gate 214 and the runner 213, which are formed in the lower platen 211. Then, the upper platen 201 is moved toward the lower platen 211 until the upper platen 201 contacts the lower platen 211 so that a space 217 is formed by the upper and lower cavities 203 and 215, and a runner 213 is formed by contacting the upper resin passage 213a to the lower resin passage 213b. As a result, the semiconductor chip 100 is located in a center of the space 217, and the lead frame 102 is sandwiched by the upper and lower platen 201 and 211. Then, the tablet 301 in the transfer pot 212 is heated until it melts completely. Then, the melted resin is pushed out from the bottom with an unillustrated plunger to the cull 202 and the runner 213 and it reaches, to the gate 214 as shown in FIG. 6C.
Referring to FIG. 6D, the melted resin passes through an opening 300 of the lead frame 102 and the gate 214, and enters the space 217. As descried above, since the semiconductor chip 100 has been placed in the space 217, it is encapsulated with the melted resin. Then, the melted resin is further heated for a particular period and solidifies as it cools down to room temperature.
After the melted resin is solidified, surplus resin remaining in the runner 213 and the cull 202, is detached from the resin solidified in the space 217 at the gate 214 so as to complete the semiconductor device 101.
However, residual burrs of the surplus resin sometimes remain in the opening 300 of the lead frame 102, because of a requirement of the gate shape. That is, since the surplus resin remained in the runner 213 should be detached from the gate to complete the semiconductor device, the size of the gate 214 should as be small as possible to permit the surplus resin to be broken easily. For this purpose, the forward region 213b″ of the lower resin passage 213b is formed thinner than other region.
As a result of this configuration, residual burrs may remain, as illustrated in reference to FIGS. 7A through 7D. For example, a residual burr 111 of the surplus resin may remain at one side of the runner 213 (FIG. 7A), or a residual burr 112 of the surplus resin may remain in the runner 213 (FIG. 7B). Also, a residual burr 113 of the surplus resin may remain at both sides of the runner 213 (FIG. 7C). A further possibility is that a residual burr 114 of the surplus resin may remain at the gate 214 (FIG. 7D).
Therefore, a deflashing process for removing the residual burrs is required when the resin shielding semiconductor device is manufactured by the molding apparatus described above.